80 MANAGEMENT OF GREENHOUSE PLANTS , 



plants ) it is therefore requisite, that in taking; plants 

 into our rooms, we should attend to these particulars. 



The internal structure of plants is composed of 

 minute and imperceptible pores, which serve the same 

 important purpose in the vegetable as veins in the 

 animal system ; they convey the circulation of the sap 

 in the former, as the veins do that of the blood in the 

 latter ; but it is by no means settled as yet by physio- 

 logists how the food of plants is taken up into the 

 system and converted into their constituent parts. 



From the foregoing considerations and facts, it is 

 evident, that, as air, heat, and moisture, are each es- 

 sential to vegetation, that water should only be given 

 in proportion as heat and air are attainable. In the 

 summer season green-house plants may be exposed 

 to the open air, from the early part of May, until the 

 end of September, by being placed on the ledges of 

 windows, or on a stand erected for the purpose, or in the 

 absence of a nursery bed of flowering plants, they 

 may be introduced into the regular flower-beds, to 

 supply the place of such plants as may wither and die 

 in course of the summer, by being turned out of the 

 pots and planted, or plunged in the earth with the 

 pots. 



In the heat of the summer season, plants generally 

 require water every evening, and in the absence of 

 dews, the earth about their roots may sometimes need 

 a little early in the morning ; but experience shows, 

 that the roots of plants more frequently get injured from 



